1. Field of the Invention
The present invention relates to miner cutting bit holders and, in particular, to miner bit holder which includes a bit holder attached to a rotating cutting drum and which receives a pressed-in replaceable sleeve for rotatably receiving a cutting bit.
2. Description of the Invention Background
In the materials mining industry, it is typical to employ a mining apparatus which includes a vertically moveable rotating cutting drum which has cutting bits attached thereto. By virtue of the rotation of the cutting drum and the movement of the miner into the material to be mined, the material is removed for further processing.
It is well known that such cutting bits and their holders are subjected to considerable stresses during the mining operation. Such stresses occur axially, vertically and transverse relative to the cutting bit. Accordingly, in normal mining operations, cutting bits require frequent replacement due to wear or breakage. In fact, cutting bits must often be replaced on a daily basis. In view of these conditions, much effort has heretofore been directed to the provision of readily replaceable cutting bits which may be removed with a minimum of effort from their supports.
Because the bit holding devices are not the primary vehicles by which material is removed from the mine face, the service life. As such, bit holding systems have been developed which include a bit holder which retains the cutting bit and which may be mounted into the miner's cutting drum. While such bit holders typically allow the cutting bit to rotate to avoid uneven wear on the bit, they may alternatively, fix the cutting bit in one position. Nevertheless, the bit holders themselves are subject to considerable wear at the mine face and their breakage may require replacement on two to six month intervals. Further, when the bit holders are designed to allow bit rotation, such relative movement quickly wears the holding surfaces of the bit holder thereby rendering them unusable. It is well known that replacement of bit holders results in considerable expense and down time for the capital intensive mining machinery.
In an effort to address these problems, bit holding devices have been developed which include a replaceable sleeve disposed between the bit holder and the cutting bit. The use of these sleeves extends the life of the bit holders by limiting the internal wear to which the bit holder is subjected. In the past, sleeves have been either freely rotatable within the bit holder, or they have been permanently fixed in one position relative to the bit holder. The sleeve of the rotatable type has a longer service life than a nonrotatable sleeve due to even wearing on sleeve surfaces which contact the mine face. However, rotatable sleeves wear and ultimately destroy the internal surfaces of the bit holders in which they rotate.
Reference is made to my copending application Ser. No. 578,972, filed on the same date as the present application, entitled "Cutting Bit Holding Apparatus", which is directed to analogous concerns as this application and whose disclosure is hereby incorporated herein by reference.
In the past, certain non-rotatable sleeves have been held in place by means of an interference fit along the entire length of the sleeve. With this type of interference fit it is difficult, if not impossible, to remove the sleeve in the field. For example, forces in excess of 72,000 lbs. are necessary to remove some sleeves. Forces of such magnitude may not reasonably be generated in the extreme environments in which such cutting bits are used. I find that it would not be practical to provide an interference fit along the entire length of the sleeve which would allow its reasonable removal because the manufacturing tolerances which would be so required would be quite cost-prohibitive.
In certain applications, others have attempted to provide an interference fit directly between the bit holder and a cutting bit. Although Applicant believes these solutions are unsatisfactory because no sleeve is provided to prevent excessive wear on the bit holder, such configurations are shown in McLennan (U.S. Pat. No. 2,800,302) and Galorneau et al. (U.S. Pat. No. 3,143,177). Applicant is of the view that an additional fundamental flaw in those designs prohibits their use in mining bits which are subjected to massive axial loads. In those designs, the interference fits are formed by two (2) conical surfaces on the bit which engage a bore in the bit holder. However, because there is no shoulder provided to resist axial forces encountered during cutting, it is believed that the axial forces encountered in mining applications will cause the conical surfaces to split the bit holder.
Therefore, Applicant has discovered the need for a non-rotatable sleeve which will not cause excessive wear or destruction of the bit holder but which can be removed easily and quickly while the miner is in service conditions.